The long-term objective of this research proposal is to understand the underlying basis for the immune abnormalities associated with age. The specific Aims are to determine qualitative as well as quantitative changes in the B lymphocytes from aged animals. The studies will focus on the age associated intrinsic defects in B cells and on the changes in the B cell heterogeneity. Subpopulations of B lymphocytes will be analysed by immunofluorescence techniques in conjunction with a fluorescence activated cell sorter and monoclonal antibodies against B cell surface molecules. Functional assays will include analysis of the B cell proliferation and differentiation in response to various anti-receptor antibodies and lymphokines. The hypothesis that the increased auto-antibody production in aged animals is the regult of abnormal representation of a unique B lymphocyte subpopulation will be tested. Seven VH gene probes that have been shown to identify all of the murine heavy chain variable region gene families will be employed. Expression of these genes will be determined by analysis of labelled RNA from mitogen activated B cells from young and old animals. Relative representation of each of the VH gene families will also be determined in purified antigen specific B cells. Any differences in the repertoire will be confirmed by construction of hybridomas and analysis of the VH gene useage by Southern blot hybridization techniques. These studies will be instrumental in defining the age associated changes that are intrinsic to B cell populations and may help devise strategies to favorably modulate the immune responses to aged individuals.